1. Field of the Invention
The present invention relates to a radio telephone apparatus, such as a hand-free type land mobile radio telephone apparatus.
2. Description of the Related Art
A connectional hand free type land mobile radio telephone apparatus has a system configuration thereof as shown in a schematic diagrammatic view of FIG. 9. As can be seen from FIG. 9, a microphone unit 1 for inputting speech voices to be transmitted and a speaker unit 2 for outputting received speech voices are connected to a suppressing circuit unit 4 provided in a radio telephone apparatus body 3 for suppressing singing or the like, and a radio telephone circuit 5 provided in the radio telephone apparatus body 3 is connected to an antenna 6.
The aforementioned type of conventional hand-free type radio telephone apparatus is installed in a vehicle in the manner shown in FIG. 10. As can be seen in FIG. 10, the microphone unit 1 is provided near a driver's seat 11, i.e., it is supported on a sun visor 13 provided on a wind shield 12 above and in front of the driver's seat 11. The microphone unit 1 is connected to the radio telephone apparatus body 3 provided at a desired site via a microphone cable 14 installed along, for example, an inner wall of the vehicle so that a speech voice made by the driver can be input to the radio telephone apparatus body 3 via the microphone cable 14. At the central portion of the vehicle and near the driver's seat 11 is provided the speaker unit 2, which is connected to the radio telephone apparatus body 3 via a speaker cable 15 so that the signal received by the radio telephone apparatus body 3 can be output in the form of a voice from the speaker unit 2. A cigar lighter socket 16 is provided at the central portion of the vehicle and near the driver's seat 11, and a power source plug 18 provided at one end of a power source cable 17 is connected to the cigar lighter socket 16. The other end of the power source cable 17 is connected to the radio telephone apparatus body 3. Consequently, power is supplied from the cigar lighter socket 16 to the radio telephone apparatus body 3 via the power source cable 17. The microphone unit 1 may be provided at a site other than on the sun visor 13 where it does not interrupt the driver's driving operation and where it can input the driver's speech voices, e.g., it may be provided near a steering column 20 for supporting a steering wheel 19. The speaker unit 2 may also be provided at a site other than the aforementioned one under the same conditions as those of the microphone unit 1.
In the conventional land mobile radio telephone apparatus having the aforementioned structure, a speech voice made by a speaker, i.e., of a driver 7, is input from the microphone unit 1 to the radio telephone circuit 5 of the land mobile radio telephone apparatus body 3 through the suppressing circuit 4 for suppressing singing caused by sound coupling between the speech voice to be transmitted and the received speech voice. The speech voice which has been processed for transmission by the radio telephone circuit 5 is transmitted from the antenna 6 to a remote speaker via a land mobile telephone station. The speech voice from the remote speaker is received by the radio telephone circuit 5 via the land mobile telephone station. The received speech voice is passed through the path opposed to that mentioned above and is output from the speaker 2 so that the driver 7 can listen to it.
In the interior of the vehicle, the power source cable 17, the microphone cable 14 and the speaker cable 15 are externally led from the radio telephone apparatus body 3. Among these cables, the microphone cable 14 is longest, and must thus be installed at a site where it does not interrupt the driver's driving operation. Hence, the microphone cable 14 is fixed at a site where it does not degrade the driver's visibility and where it does not come off by the vibrations generated during travel. However, installation of this microphone cable 17 is a troublesome work. The microphone cable 14 which comes off from its fixed site due to vibrations generated during travel or the like may interfere with the driving operation.
Furthermore, since the radio telephone apparatus body 3 is supplied with power from the cigar lighter socket 16 in the vehicle, when the land mobile telephone apparatus is used in another vehicle, the power source cable 17 is also required. This makes fixing of the power source cable 17 in the vehicle impossible. When the land mobile radio telephone apparatus is used in another vehicle, the speaker 2 and the speaker cable 15 must also be moved together with the radio telephone apparatus body 3 and be installed at a site where they do not interfere with the driver's operation, which is a troublesome work. Removal of the speaker cable 15 due to vibrations generated during travel interferes with the driver's driving operation and makes driving a dangerous work.
In such a land mobile radio telephone apparatus, telephone calls are generally made while the vehicle is travelling. In that case, telephone conversations are frequency made without the use of a hand-held handset from the viewpoint of safety of driving. However, in that case, since the microphone 1 and the speaker 2 are spaced from each other, if a telephone call is made at a site of a heavy traffic, conversations may be transmitted to the other party together with an undesired noise generated around the microphone unit 1, thus greatly deteriorating the S/N ratio of the aural signal received by the other party and thus making communications between two parties difficult. The telephone conversations made without use of a hand-held handset while the vehicle is at a stop may also be buried in the background noise.
Furthermore, in the conventional radio telephone apparatus, since the distance between the user 1 and the microphone unit 1 is longer than in the normal case where telephone conversations are made using a handset, an undesired noise in the interior of the vehicle are input to the microphone unit 1 together with the telephone conversations. The input noise is mixed into an aural signal and such an aural signal is transmitted to the other party, thus deteriorating the S/N ratio of the signal and making communications difficult.